The invention relates to coated glass and, in particular, to visible light reflecting, solar control coated glass articles.
Coatings on architectural glass are commonly utilized to provide specific energy absorption and light transmittance properties. Additionally, coatings provide desired reflective or spectral properties that are aesthetically pleasing. The coated articles are often used singularly or in combination with other coated articles to form a glazing or window unit.
Coated glass articles are typically produced xe2x80x9con-linexe2x80x9d by continuously coating a glass substrate while it is being manufactured in a process known in the art as the xe2x80x9cfloat glass process.xe2x80x9d Additionally, coated glass articles are produced xe2x80x9coff-linexe2x80x9d through a sputtering process. The former process involves casting glass onto a molten tin bath which is suitably enclosed, thereafter transferring the glass, after it is sufficiently cooled, to lift out rolls which are aligned with the bath, and finally cooling the glass as it advances across the rolls, initially through a lehr and thereafter while exposed to the ambient atmosphere. A non-oxidizing atmosphere is maintained in the float portion of the process, while the glass is in contact with the molten tin bath, to prevent oxidation of tin. An oxidizing atmosphere is maintained in the lehr. In general, the coatings are applied onto the glass substrate in the float bath of the float bath process. However, coatings may also be applied onto the substrate in the lehr.
The attributes of the resulting coated glass substrate are dependent upon the specific coatings applied during the float glass process or an off-line sputtering process. The coating compositions and thicknesses impart energy absorption and light transmittance properties within the coated article while also affecting the spectral properties. Desired attributes may be obtainable by adjusting the compositions or thicknesses of the coating layer or layers. However, adjustments to enhance a specific property can adversely impact other transmittance or spectral properties of the coated glass article. Obtaining desired spectral properties is often difficult when trying to combine specific energy absorption and light transmittance properties in a coated glass article.
There is an increasing demand for solar control glasses, especially high performance solar control glasses that exhibit a neutral color in both reflection and transmission. xe2x80x9cHigh performancexe2x80x9d solar control glasses means glasses that transmit a significantly higher percentage of incident light than of total incident radiation energy (total solar heat).
It would be advantageous to provide a coated stack for a glass article that is itself color neutral, so that for the coated glass article, the reflected color from the film side is neutral, and transmitted color remains substantially unchanged from that of the selected base glass. A visible light reflecting, solar control glazing with a low emittance, and a low solar heat gain coefficient, would significantly improve energy costs in buildings and homes while providing a desirable neutral color for, at least, film side reflection. The low emittance characteristic of the glazing would minimize any indirect heat gain from absorption.
According to the invention there is provided a visible light reflecting, solar control article comprising a glass substrate, a first coating deposited over the glass substrate and a second coating deposited over the first coating. The first coating is comprised of a doped metal oxide, and in an especially preferred embodiment is comprised of fluorine doped tin oxide. The first coating provides the low emissivity of the coated glass article.
The second coating is comprised of a transparent metal oxide having a refractive index greater than the refractive index of the first coating. The addition of the second coating increases the visible light reflectance of the coated glass article, so that the resulting coated glass article has a film side reflectance Rf greater than 15% and an emissivity less than or equal to about 0.3.
Preferably, the coated glass article includes an iridescence-suppressing interlayer deposited between the glass substrate and the first coating of the doped metal oxide. The coatings are such as to provide a neutral color in transmittance and reflectance when applied to a clear glass substrate.